The global battle raging over the Canadian tar sands had a dramatic homecoming on Monday. Hundreds of Canadians – among them environmentalists, union members and native leaders – converged on Ottawa's Parliament Hill to protest the Conservative government's aggressive promotion of the Keystone XL pipeline and the Albertan industry widely castigated as the world's most environmentally destructive.

In waves, about 200 people crossed a 3ft fence marking a restricted police zone to symbolically deliver a message to Canada's Prime Minister. Most were detained and later released with trespassing tickets. The beat of a native drum kept supporters buoyant, gigantic fake syringes reading "tar sands junkie" bobbed in the crowd, and Raging Grannies belted out spirited renditions of classic protest songs with oily twists.

The Canadian action heralds a new spirit of defiance in the broader climate change movement. It follows on two weeks of sit-ins at the White House in Washington last month where more than 1,200 people were arrested over Keystone XL – the TransCanada pipeline that would carry the dirty Alberta oil to Texas refineries. The Washington protesters successfully introduced millions of Americans to their No 1 source for oil imports, putting an ecological-disaster zone the size of Florida on the map; now, their Canadian counterparts showed they were neither silent nor passive on the issue. These are signs that the environmentalist community – professionalised and tame for too long – may have discovered a much-needed impetus for civil disobedience.

This has accomplished an end possible only when the powerful are confronted by direct action: it has brought to the surface the hidden tensions and costs behind the Keystone XL project, exposing them to public scrutiny. The opposing camps are no longer simply battling for the hearts and minds of North Americans over a pipeline, but on the more essential question of the future of continental energy use. The contending visions offer us a stark choice: to relentlessly drill and dig for the deepest and dirtiest fossil fuels, or to promote a sustainable, cleaner future of renewable power from the sun, wind and waves.

Canadian Prime Minister Stephen Harper's description of the Keystone XL pipeline decision as a "no-brainer" is a crude illustration of his government's position: a mixture of hubris and recklessness that embraces an era of extreme energy use and runaway climate change. His friends in the Alberta oil patch have set their hopes on scraping every last dollar's worth of bitumen from the ground: 4-5m barrels a day by the end of the decade, continuing until 97% of oil yet to be developed is gone and untold carbon emissions have been released. Alberta Energy Minister Ron Liepert has expressed the need for more pipeline infrastructure as a provocation: "By 2020, we may need three Keystones," he told the Financial Times

But the heavy police presence, designed to tackle up to 8,000 protesters, and miles of fence that surrounded Ottawa's Parliament on Monday were a physical manifestation of the Canadian government's growing anxiety. Natural Resources Minister Joe Oliver conceded that the protests are a "major concern". Since 2010, as discovered by "access-to-information" [freedom of information] requests I have made, the prime minister's office has convened secret high-level meetings involving the cabinet to address the "escalating pressure" from the climate movement; further disclosures have been delayed by government officials.

With only months before a decision over the Keystone XL is expected from Secretary of State Clinton, there are signs of a gathering storm of potentially decisive opposition. Protesters in Idaho are being arrested for blocking the shipment to Alberta of tar sands equipment called "megaloads"; legal challenges over endangered species that could further tie up the pipeline project are in the works; and there is the makings of a crucial fight over sovereignty between the State Department and native Americans, signalled last week in an anti-Keystone XL accord signed on the Rosebud Sioux reservation. Others plan to be a noisy presence at State Department public hearings, as well as following President Obama's campaign touring and targeting his campaign offices. On 6 November, exactly a year before the next election, thousands plan to encircle the White House in a human chain of protest.

The promise of this growing focus for the climate movement, as with the recent Occupy Wall Street, lies partly in its impulse to pick up where the global justice movement left off: zoning in on the spaces of the elite responsible for the crisis, and transforming them into a place of dissent. Routes for pipelines, roads for mega-loads, hallways for lobbyists – the infrastructure of fossil fuels corporate magnates and their government enablers – may be turning into the site of historic and necessary confrontation.

• This article originally stated that 8,000 police officers guarded the Parliament in Ottawa on Monday; in fact, a substantial police force designed to cope with up to 8,000 protesters attended. This was amended at 2pm EST (7pm UK time) on 28 September 2011.